Structure and clumping in the fast wind of NGC6543

Abstract

Far-UV spectroscopy from the FUSE satellite is analysed to uniquely probe spatial structure and clumping in the fast wind of the central star of the H-rich planetary nebula NGC6543 (HD164963). Time-series data of the unsaturated PV 1118, 1128 resonance line P Cygni profiles provide a very sensitive diagnostic of variable wind conditions in the outflow. We report on the discovery of episodic and recurrent optical depth enhancements in the PV absorption troughs, with some evidence for a 0.17-day modulation time-scale. SEI line-synthesis modelling is used to derive physical properties, including the optical depth evolution of individual `events'. The characteristics of these features are essentially identical to the `discrete absorption components' (DACs) commonly seen in the UV lines of massive OB stars. We have also employed the unified model atmosphere code CMFGEN to explore spectroscopic signatures of clumping, and report in particular on the clear sensitivity of the PV lines to the clump volume filling factor. The results presented here have implications for the downward revision of mass-loss rates in PN central stars. We conclude that the temporal structures seen in the PV lines of NGC6543 likely have a physical origin that is similar to that operating in massive, luminous stars, and may be related to near-surface perturbations caused by stellar pulsation and/or magnetic fields.

11 pages, 11 figures. Accepted for publication in MNRAS

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• On the X-ray temperature of hot gas in diffuse nebulae
• NLTE Model of NGC 6543's Central Star and its Relation with the Surrounding Planetary Nebula
• Planck intermediate results. XVIII The millimetre and sub-millimetre emission from planetary nebulae
• PN fast winds: Temporal structure and stellar rotation
• Narrow Radiative Recombination Continua: A Signature of Ions Crossing the Contact Discontinuity of Astrophysical Shocks
• Looking deep into the Cat's Eye: Structure and rotation in the fast wind of the PN central star of NGC6543
• Raman Scattered HeII 6545 in the Young and Compact Planetary Nebula NGC 6790
• HST STIS observations of the mixing layer in the Cat's Eye Nebula
• The dense and asymmetric central star wind of the young PN He 2-138
• The gas turbulence in planetary nebulae: quantification and multi-D maps from long-slit, wide-spectral range echellogram
• Optically-thick Structure in Early B Type Supergiant Stellar Winds at Low Metallicities